1. Field of the Invention
The present invention relates to indium antimonide photodiodes. It also relates to the different methods for manufacturing these photodiodes.
The present invention aims at solving the following problem:
on the one hand, construction of photodiodes for infrared operation on an indium antimonide semiconductor substrate;
on the other hand, coupling of these photodiodes with a charge transfer device for multiplexing the photodiodes and reading out the charges; this device is formed on a semiconductor substrate, generally made from silicon, and has an N channel. The use of an N channel device, formed on a P type substrate, allows very good charge injection efficiency to be obtained as well as high mobility of the minority carriers of the device which are electrons.
2. Description of the Prior Art
Reference may be had for example to the article published in the review I.E.E.E. volume ED 27, No. 1, January 1980, pages 175 to 188, which is entitled "CCD Readout of infrared hybrid focal-plane arrays". This article shows an N channel charge transfer device coupled to a photodiode--see FIGS. 2 and 5 and the corresponding comments.
In the prior art, photodiodes were formed on an N type indium antimonide substrate. For connecting these photodiodes to an N channel charge transfer device, an additional current source had to be used as is described in French patent application No. 81.12841 in the name of Thomson-CSF. In fact, in the case of a photodiode network formed on an N type substrate, the N substrate is common to all the photodiodes and only the P regions of the photodiodes may be connected to the N channel of the charge transfer device. As is explained in the above mentioned patent, in this case the charges coming from the photodiodes are of the opposite sign to those transferred into the charge transfer device. An additional current source has therefore to be used which injects into the charge transfer device a current which may be written: a-s, where a is a current supplied by the source and s the current coming from a photodiode.
These additional current sources are difficult to construct and complicate the assembly of the device.
The present invention overcomes the above mentioned problem in a simple and efficient way.